The present invention relates to an improved method of blowing bottles with finished necks wherein intermittent extrusion blow molding apparatus is employed.
It is conventional practice to utilize apparatus of this character to form bottles with necks that are trimmed and compression molded at the extrusion station, as is disclosed, for example, in U.S. Pat. No. 3,470,582, issued Oct. 7, 1969 to Martin, Jr., entitled "Apparatus for Compacting and Trimming Necks in Blow Molded Containers". As is disclosed in this patent, when forming bottles with a small neck, it is inherent with the apparatus used that the extruded parison will have a diameter greater than the neck of the blown bottle so that when the mold halves are closed on the parison, flash is formed on opposite sides of the neck and shoulders of the bottle and must subsequently be trimmed from the bottle, leaving blemishes or flash marks. These marks are undesirable in bottles used in certain industries, such as the cosmetics industry, so that when supplying these industries with bottles, other blow molding practices must be followed which produce bottles which are free from flash marks on the exterior surfaces and particularly on the neck. Not only is this requirement made for reasons of appearance, but also to assure that optimum sealing conditions exist between the threaded neck of the bottle and the closure cap.
Various procedures and apparatus are known in the blow molding industry for forming bottles which meet requirements relating to appearance, but these procedures are not fully adequate to meet the demands of industry for bottles that have the desired finsihed neck, and that also have a desired neck wall thickness for allowing a fill tube to enter the bottle and function properly, and that can be produced at a minimum cycle time so as to provide bottles of the desired quality at a minimum of cost.